Bacteriorhodopsin (bR) is well recognized for its applied values. We observed that the bottleneck associated with the use of different peptones for bR production was linked to the presence of tryptophan (Trp). Trp at 0.36 mM in the culture medium inhibits bR formation. The results obtained in this study demonstrate that bR content (mg l(-1)) of Halorubrum sodomense A01 decreased to 2.9 mg l(-1) in 0.36 mM Trp compared to control (0.11 mM Trp) where 12.3 mg l(-1) of bR was obtained. Our results provide useful information for the design of production conditions for bR to be used in applied settings.